Chemistry Notes
Chemical Quantities Chapter 7 Addison-Wesley
Here is a list of material included on the test. Some will be vocabulary and many will be
related to mathematical conversions using the Mole Road Map and a Periodic Table.
Since atoms and molecules are too small to be counted directly, another method has been
developed which allows students and scientists to measure matter accurately. The
method involves “the mole.” To get a mole of a substance, find the atomic mass or
molecular mass using a periodic table and then trade the u (atomic mass unit) for g
(grams). Then you have one mole of the substance. Just use a balance to measure out a
mole of the substance.
A mole of any element is 6.02 x 1023 atoms of that element. Whatever the material, a
mole is 6.02 x 1023 representative particles of that substance. It could be molecules,
formula units, tables, dogs, squirrels, anything.
Representative particle refers to the species present in a substance. Example: atoms,
molecules, eggs, etc.
Avogadro’s number - 6.02 x 1023
The Gram Formula Mass
The Molar Mass of a Substance – trade u for g
Mole-Mass Conversions – be able to convert (you may use the road map)
The Volume of a Mole of Gas at STP is 22.4 L. It doesn’t matter what kind of gas as
long as it is at Standard Temperature and pressure (STP).
Converting between units with moles
Calculating Percent Composition – first find the molar mass of the individual
elements in a compound. Then add them up to find the molar mass of the compound.
Take the element mass, divide by the compound mass, and multiply by 100 to get the
percent composition of each element. When added together, they should sum to
approximately 100%.
Molarity – this refers to the amount of solute (material) dissolved in the solvent (ie:
water). The higher the number, the more concentrated the solution. For example, a 1M
solution of HCl (hydrochloric acid) is made by taking 1 L of water, removing some of it
so there is less than one liter, adding 1 mole of HCl, then adding enough water to make
exactly 1 Liter of solution. A 2M solution would be made in the same manner but would
have 2 moles of HCl added to the water to get exactly one liter of solution.
You don’t need to calculate Empirical Formulas but you need to recognize them.
Think of empirical formulas as a reduced version just like you would reduce a
fraction. If the subscripts have a common denominator, use it to reduce.
For example: CH2 is the empirical formula for C2H4